Hm, have you gone to see the Quiggle over at the Herbology Club? And gone throguh the full conversation with him? If you have, you should get new text at the quarry to navigate as you juggle for the Jubjubs.

How many donations had you made at that point?
With people saying the got it but didn't donate each day, I'm noting that a lot of people have gotten it with more than 100 donations. Assuming it wasn't activated properly, you may need to donate X number of times. Somewhere in the 100-125 range, I'd guess.

If it's enoguh for a trophy, it's enough for an avatar. We have FAQ confirmation that trophies will be a thing, but nothing on if we'll be getting as avatar as of yet. 100 should be more than enough. :)
Also, because I've decided I'm donig this, apparently:
I'm gonna try and see what the prize rarity ranges are and how they're impacted by donation rarities. If you guys could post (preferably in batches so you're not just making a ton of posts with this) the rarity of all 5 items you donate (saying 5 r80s, or 3 r75s and 2 r76s is fine) and the rarity of the prize you get, it'll be a big help. :) Just be sure that it's clear what 5 item rarties match up with which prize.

In theory, the rarity range of the items you can get is determined by the rarity range of the items donated.
So if you donate 5 r80 items, you'll get an r80 in return. If you donate 5 items between r50 and r60, the item you get will be between r50 and r60.
Alternately, you can get things back of the range stated above plus or minus 5. So in this case donating 5 r80 items gets you things in the r75 to r85 range. Or maybe this bit only applies to r90+ items to keep people from totally gaming the system! We'll have to see.
I'll do some testing of this later, but if you want to go for expensive items, donate rare items. Also if you guys can tell me the rarity ranges of specific donations you've made and the rarity of the item you got, like some of you are all ready, it'll be a big help. More data is good!

The FAQ says you'll get a trophy and end prizes based off of "how generous you were", which I assume means based on the amount you donated. So probably a site event trophy. But who knows what the tiers will be.

I did some checking, and yes, 5 is the upper limit. So when donating, the first item can be whatever, but after that, the rarity of the next item must be between the rarity of the item before it, and that rarity plus 5 inclusive.
So, if r is the rarity of the item preceding this one, and n is the rarity of the current item to be added:
r ≤ n ≤ r+5
And the dropdowns will helpfully sort this mathy stuff out for you as you go so you can't accidentally try and donate things that aren't properly sorted. You won't even be able to make the selection.

Also, to answer the question that I missed at the bottom of the last page:
We currently don't know when or how they'll be awarding an avatar, or if there will be one. We also don't know if it will be the same as last year's or a new one if it does exist. We'll just have to wait and see. Most likely it will go to anyone who has donated some minimum requirement of items.

Yes, you can donate the same item several times. I donated 5 Yellow Tonu Folders earlier in one go.
This does include books and wearables (I missed that tidbit when I made my earlier post, since it's an offhand remark in the event description...). But the wearables all things in the cross-section between "wearable" and "school" or "clothes" or "books". And while a lot of wearables are clothing items, most clothing items aren't wearable. People are far more likely to donate the piles of cheap, unwearable clothes items laying about than expensive wearables. The same goes for books, really- people are far more likely to donate cheap junk books you can get from dailies or the BD than anything particularly expensive.
Also they've changed the donating style from last year, so JN may have just copied the old one over to start with. Instead of being "five items in this range" it's "five items, with each one being no more than 5 rarity points above the previous". So an r76 can have up to an r81 after it. (If that 5 turns out to be wrong forgive me, I haven't tested this in depth yet but it makes sense as a breaking point.)
Note that the above goes double because last year's end prizes were ridiculously little compared to the effort a lot of people put in. I'm personally going to donate several times so I get a trophy, but it'll mostly be things from my SDB and dailies fodder.

They didn't specify very well, did they? Any item with the category "School" can be donated. If you bring up an item in your inventory you'll see a "Type" field in the information. Anything that says "School" there will qualify. This is generally notebooks, folders, pencils, ect. Be careful though, if an item is r101 it's type "Special" and will not count even if it's a relevant kind of item (such as notebooks from old Advents). You can also sort your SDB by type. Selecting "School" there will bring up the relevant items (though again, take care about r101 things).

Way back when I was actively saving, a friend told me this tip:
Set it so that you have a PIN on your bank, and then only on things you want to be safe that you never use (so take it off your SDB). Then set a new PIN by hitting random numbers with your eyes closed and copy/pasting the number in without looking at it. This way you can't get NP out of the bank without sending for the PIN (try not to lose your pass) which deters a LOT of impulse spending. If you don't want to try and bash a PIN in, ask a trusted friend or relative to do it real fast while you're sitting there with them but not looking.
Alternately, invest in stocks. Then you can't spend it AND you're making more! Just remember to keep an eye on them.

The PB clothes transfer system is a bit funky, and I can see how you'd be kinda confused. It's hard to word in a sensible manner. That said, you've got the right idea for getting the clothes and pet you want moved to your side. What you detailed should work perfectly for your purposes. As for your specific questions, the short answer to both is "yes". Once the clothes are on the side account, you will only be able to move those clothes if you have a Stealthy Draik on that account and transfer it out. You won't be able to move them with a Magma or Purple or whatever other color Draik. To elaborate on how the system works (in a way that hopefully makes sense).... Basically, when a pet is transferred, the system does various checks on the pet and its clothing and items and such. Noting that I don't have exact knowledge of how they've got the backend of the site set up, my guess is that the chunk of code that handles which clothing items stay and go would go something like this:
For each article of clothing the pet has on:
Is this an NC item?
If yes:
Remove the item from the pet and place it in the current owner's closet.
If no, is this an NP item?
If yes:
Leave the clothing item on the pet, transfer as is.
If no (meaning it must be a PB item):
Check the item against the pet's color. Does this item come with this color of the pet?
If yes:
Leave the clothing item on the pet, transfer as is.
If no:
Remove the item from the pet and place it in the current owner's closet. Does this pet/color combo come with PB clothes? If yes: For each article of PB clothing this pet/color combo comes with: Does this item exist anywhere on the account? If yes: Is the pet currently wearing this item? If yes: Leave the clothing item on the pet, transfer it as is. If no:
Is the item on another pet?
If yes:
Remove the item from the other pet. Place it in a "temporary transfer closet". When the transfer is accepted, place it in the new owner's closet.
If no:
Remove the item from the closet. Place it in a "temporary transfer closet". When the transfer is accepted, place it in the new owner's closet.
I have no idea if that helped you specifically, but that's as straightforward as I can make what the system does when it comes to clothes when you transfer a pet.